try adding "" around the inc.v and path information on where it's located. i.e. `include "../../some_path/inc.v"
for modelsim this path will be relative to the current directory modelsim is running from.
Unless all your files are co-located in the simulation directory it probably won't find the inc.v file otherwise.
Also, you should place the `include inc.v line in your other files outside the module-endmodule structure.
You should also know that including the same inc.v file in a bunch of other files will result in many warnings about redefinition of a define.
I typically use a top level include file which includes all the files (except the top level) including the define file and then the `defines only get defined once.